Introduction
The satellite industry could experience its biggest revolution since it joined the ranks of commerce, thanks to some of the smallest machines in existence. Researchers are performing experiments designed to convince the aerospace industry that microelectromechanical systems (MEMS) could open the door to low-cost, high-reliability, mass-produced satellites.MEMS combine conventional semiconductor electronics with beams, gears, levers, switches, accelerometers, diaphragms, microfluidic thrusters, and heat controllers, all of them microscopic in size.

"We can do a whole new array of things with MEMS that cannot be done any other way," said Henry Helvajian, a senior scientist with Aerospace Corp., a nonprofit aerospace research and development organization in El Segundo, Calif.

Microelectromechanical Systems, or MEMS, are integrated micro devices or systems combining electrical and mechanical components. They are fabricated using integrated circuit (IC) batch processing techniques and can range in size from micrometers to millimeters. These systems can sense, control and actuate on the micro scale, and function individually or in arrays to generate effects on the macro scale.

MEMS is an enabling technology and current applications include accelerometers, pressure, chemical and flow sensors, micro-optics, optical scanners, and fluid pumps. Generally a satellite consists of battery, internal state sensors, communication systems and control units. All these can be made of MEMS so that size and cost can be considerably reduced. Also small satellites can be constructed by stacking wafers covered with MEMS and electronics components. These satellites are called 'I' Kg class satellites or Picosats. These satellites having high resistance to radiation and vibration compared to conventional devices can be mass-produced there by reducing the cost. These can be used for various space applications.Also small satellites can be constructed by stacking wafers covered with MEMS and electronics components. These satellites are called 'I' Kg

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MEMS Abstract.docx (Size: 75.29 KB / Downloads: 169)
ABSTRACT
In this paper MEMS have been described. The MEMS stands for Micro Electro Mechanical System. The paper describes about the technologies, its fabrication, use of the technology and its application in various field. MEMS have been widely used in Japan and Europe. MEMS is an emerging technology which uses the tools and techniques that were developed for the Integrated Circuit industry to build microscopic machines. These machines are built on standard silicon wafers. The real power of this technology is that many machines can be built at the same time across the surface of the wafer, with no assembly required. Since it is a photographic-like process, it is just as easy to build a million machines on the wafer as it would be to build just one.2: INTRODUCTION
Micro-Electro-Mechanical Systems, or MEMS, is a technology that in its most general form can be defined as miniaturized mechanical and electro-mechanical elements (i.e., devices and structures) that are made using the techniques of microfabrication. The critical physical dimensions of MEMS devices can vary from well below one micron on the lower end of the dimensional spectrum, all the way to several millimeters. Likewise, the types of MEMS devices can vary from relatively simple structures having no moving elements, to extremely complex electromechanical systems with multiple moving elements under the control of integrated microelectronics. The one main criterion of MEMS is that there are at least some elements having some sort of mechanical functionality whether or not these elements can move. The term used to define MEMS varies in different parts of the world. In the United States they are predominantly called MEMS, while in some other parts of the world they are called “Microsystems Technology” or “micromachined devices”.
While the functional elements of MEMS are miniaturized structures, sensors, actuators, and microelectronics, the most notable (and perhaps most interesting) elements are the microsensors and microactuators. Microsensors and microactuators are appropriately categorized as “transducers”, which are defined as devices that convert energy from one form to another. In the case of microsensors, the device typically converts a measured mechanical signal into an electrical signal.
MEMS are separate and distinct from the hypothetical vision of molecular electronics. MEMS are made up of components between 1 to 100 micrometres in size (i.e. 0.001 to 0.1 mm) and MEMS devices generally range in size from 20 micrometres (20 millionths of a metre) to a millimetre. They usually consist of a central unit that processes data, the microprocessor and several components that interact with the outside such as microsensors. At these size scales, the standard constructs of classical physics are not always useful. Because of the large surface area to volume ratio of MEMS, surface effects such as electrostatics and dominate volume effects such as inertia or thermal mass.
The potential of very small machines was appreciated before the technology existed that could make them—see, for example, Richard Feynman's famous 1959 lecture. There's Plenty of Room at the Bottom. MEMS became practical once they could be fabricated using modified semiconductor device fabrication technologies, normally used to make electronics. These include molding and plating, wet etching (KOH, TMAH) and dry etching (RIE and DRIE), electro discharge machining (EDM), and other technologies capable of manufacturing small devices. An early example of a MEMS device is the resonistor – an electromechanical monolithic resonator.3: MATERIALS FOR MEMS MANUFACTURING
Silicon
Silicon is the material used to create most integrated circuits used in consumer electronics in the modern world. The economies of scale, ready availability of cheap high-quality materials and ability to incorporate electronic functionality make silicon attractive for a wide variety of MEMS applications. Silicon also has significant advantages engendered through its material properties. In single crystal form, silicon is an almost perfect Hookean material, meaning that when it is flexed there is virtually no hysteresis and hence almost no energy dissipation. As well as making for highly repeatable motion, this also makes silicon very reliable as it suffers very little fatigue and can have service lifetimes in the range of billions to trillions of cycles without breaking. The basic techniques for producing all silicon based MEMS devices are deposition of material layers, patterning of these layers by photolithography and then etching to produce the required shapes.
Polymers
Even though the electronics industry provides an economy of scale for the silicon industry, crystalline silicon is still a complex and relatively expensive material to produce. Polymers on the other hand can be produced in huge volumes, with a great variety of material characteristics. MEMS devices can be made from polymers by processes such as injection molding,embossing or stereolithography and are especially well suited to microfluidic applications such as disposable blood testing cartridges.
Metals
Metals can also be used to create MEMS elements. While metals do not have some of the advantages displayed by silicon in terms of mechanical properties, when used within their limitations, metals can exhibit very high degrees of reliability.
Metals can be deposited by electroplating, evaporation, and sputtering processes. Commonly used metals include gold, nickel, aluminium, copper, chromium, titanium, tungsten, platinum, and silver.4: MEMS MANUFACTURING TECHNOLOGIES
Bulk micromachining
Bulk micromachining is the oldest paradigm of silicon based MEMS. The whole thickness of a silicon wafer is used for building the micro-mechanical structures. Silicon is machined using various etching processes. Anodic bonding of glass plates or additional silicon wafers is used for adding features in the third dimension and for hermetic encapsulation. Bulk micromachining has been essential in enabling high performance pressure sensors and accelerometers that have changed the shape of the sensor industry in the 80's and 90's.

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N.NAGENDRA REDDYMEMS.docx (Size: 97.31 KB / Downloads: 104)
Abstract:
Micromachining and micro electro mechanical systems (MEMS) technologies can be used to produce complex structure, devices, and systems on the scale of micrometres. MEMS is the integration of mechanical elements, sensors, actuators and electronics on a common silicon substrates through microfabrification technology. MEMS is an enabling technology allowing the development of smart products, augmenting the computational ability of microelectronics with the perception and control capabilities of microsensors and microactuators and expanding the space of possible designs and applications. There are numerous possible applications for MEMS. As a breakthrough technology, allowing unparalled synergy between previously unrelated fields such as biology and microelectronics, many new MEMS applications will emerge, expanding beyond that which is currently identified or known. This paper reviews the scope of technology and the application it addresses. It includes a short analysis of future opportunities. This paper also describes the micromachining techniques used in the fabrication of MEMS.
Keywords:
Micromachining, Microsystems, Piezoelectric actuation, Electrostatic actuation, Thermal actuation, Magnetic- actuation. 1. INTRODUCTION
Micromachining and Micro-Electro-Mechanical Systems (MEMS) technology can be used to produce complex structure, devices, and systems on the scale of micrometers. Micromechanical structures and systems are miniturised devices that enable the operation of complex systems. They exist today in many environments, especially medical, consumer, industrial and aerospace. Their potential for penetration into a broad range of applications is real, supported by strong developmental activities at many companies and institution. The technology consists of large portfolio of design and fabrication processes, many borrowed from integrated circuit industry. The development of MEMS is inherently interdisciplinary, necessitating an understanding of MEMS components as well as end applications. Due to the enormous breadth and diversity of the devices and systems that are being miniaturized, the acronym MEMS is not particularly apt one (i.e. the field is more than simply micro, mechanical and electrical systems). Other names for this general field of miniaturization include Microsystems technology (MST), popular in Europe, and micromachines, popular in Asia2. MICROMACHINING
The needs for miniaturization of various ultra precision items utilized for producing highly precision machines and equipment necessitate the development of manufacturing process capable of performing micromanufacturing activities. The emergence of MEMS has strongly enhanced the use of fewer and harder materials, brittle materials and their micromachining technologies. A set of new technologies useful for successful international competitive development is micromachining, which satisfy many of the present industrial needs in the manufacturing. According to CIRP committee of Physical and Chemical machining Processes, “machining,” means machining the dimensions in the range of 1_199 um.
Although many of the microfabrication techniques and materials used to produce MEMS have been borrowed from the IC industry, the field of MEMS also driven the development and refinement of other microfabrication processes and materials not traditionally used by the IC industry. This paper briefly reviews selected micro machining processes capable of sub-micron structure to large structure micro. Large numbers of micro machine processes or presently used for the various kinds of applications.2.1 REVIEW OF LARGE STRUCTURE MICROMACHINING TECHNIQUES
Process utilizing tool as in conventional machining process hardly achieve small amount of hard material removal by mechanical force or shear or shear phenomenon. The machinable size is also limited because of the elastic deformation of micro tool or work piece. These processes are only suitable for 3D products and hardly achieve unit removal at atomic level. On the other hand Non-conventional Machining processes using tool or tool in the form of shape i.e. Electro Discharge Micromachining (EDMM). Laser Beam Machining (LBM), Ultrasonic Micromachining (USMM). Abrasive Jet Machining (AJM) etc. which has been very successful in the large structure micromachining inherently achieves very small unit removal. These processes have been found to be very suitable for micromachining because of having remarkable advantages. Machining force in these processes such as than that of in conventional machining processes such as cutting, milling, drilling etc. Metal chips can be removed with a very small force in processes such as EDM, USM and LBM etc
[/b]2.2 REVIEW OF SUB-MICRON MICROMACHINING TECHNIQUES
The majority of sub-micron micromachining procedures involve two types of interaction; electromagnetic radiation (e.g. optical, UV or X-ray photons) or charged particles (electronics, low energy heavy ions, high energy light ions) In general the micromachining procedures based on electromagnetic radiation require masks. In mask processes a selective pattern of radiation is transmitted through a structured mask on to a resist material, and subsequent development of the exposed resist using specific chemicals can produce microstructures. The use of charged particle techniques for micromachining therefore is essentially limited to direct write processes, where a focused charged particle beams is scanned over a material in a specific pattern to produce microstructures. Although the detect write processes has the advantage that masks are not required, it has an obvious limitation in that the production of micro components is a serial process that has greatly reduced efficiency for multiple component production(4).Optical lithography, X-ray lithography (LIG),deep UV lithography, electron beam direct writing are some of the widely used sub-micron micromachining methods. The vast majority of methods are condensed into three major categories:
1. Material deposition, including thin film deposition and bonding processes.
2. Pattern definition using lithography.
3. Etching.
Different sub-micron micro machining techniques have been summarized in the Table 1 and 2.3. MATERIALS FOR MEMS
The choice substrate materials for MEMS are very broad, but crystalline silicon is by far, the most common. Complementing silicon is a host of materials that can be deposited as thin films. These include polysilicon, amorphous silicon, silicon oxides and nitrides, glass, and organics polymers as well as host of metals. Crystallographic plane play important role in the design and fabrication of silicon based MEMS and also affect some mechanical properties of Silicon. Three physical effects commonly used in the micromechanical sensor and actuators: Piezoresistivity, piezoelectricity and thermoelectricity4. MICRO SYSTEM COMPONENTS
A micro system will typically comprise of components from one or more of the three classes: microsensors, to detect changes in the system's environment; an intelligent component that makes decisions based on changes detected by the sensors; and microactuators, by which the system changes its environment. The basic sensing and actuation system vary considerably from one design to another, with significant consequences to control electronics. Design considerations are many; they include specifications of end applications, functionality, process feasibility and economics justification.
Three general categories from the total extent of the MEMS: sensors, actuators and passive structures. Sensors are the transducers that convert mechanical, thermal are any other form of energy into electrical energy; actuators do actually the opposite 4.1 TECHNIQUES FOR SENSING AND ACTUATION
Micromachining and MEMS are the technologies well suited to improve the performance, size and cost of the sensing system. For this reason the greatest commercial successes in MEMS are microsensors and they represent the majority of MEMS developed to date. Although historically, the greatest demand and most research and development activity has been on pressure sensor and accelerometers, the field of MEMS is maturing and the diversity of the applications and sensor technologies has been increased tremendously. The actuation option available in MEMS are strain gauges, capacitive position detectors, pressure sensors, inertial sensors, magnetometers, thermal sensors, chemical sensors, polymer based gas sensors, resonant sensors, electrochemical sensors, molecular -specific sensors, cell based sensors etc. although it is impossible to describe each micro sensor technology in detail the most prominent microsensors technologies are described

ABSTRACT
• Micro Electro Mechanical Systems (MEMS) in the field of biomedical industry has given rise to Bio MEMS. These encompasses Biosensors, Bio instruments and tools, Bio testing and analysis etc
• Bio MEMS present a great challenge to engineers to design and manufacture of these types of sensors and instruments serves as the interface between living and electronic systems.
• These systems and the sensors should not affect the behavior of the living systems.
• Thin – film microelectronic technology offers special advantages for manufacturing of Biosensors over the traditional manufacturing methods.
• These can be used in minimizing the deleterious interactions through the use of small size and mass, Bio compatible material, and physical characteristics that are closely related to living tissues.
• Not only Bio MEMS the finger print sensor also discussed in this paper.What are MEMS ?
(Micro-electromechanical Systems)
• Fabricated using micromachining technology
• Used for sensing, actuation or are passive micro- structures
• Usually integrated with electronic circuitry for control and/or information processing

Micro-Electro Mechanical or microelectronic and micro-electro mechanical systems is the technology of very small mechanical devices driven by electricity; it merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are also referred to as micromachines (in Japan), or Micro Systems Technology - MST (in Europe).
MEMS are separate and distinct from the hypothetical vision of molecular nanotechnology or molecular electronics. MEMS are made up of components between 1 to 100 micrometres in size (i.e. 0.001 to 0.1 mm) and MEMS devices generally range in size from 20 micrometres (20 millionths of a metre) to a millimetre. They usually consist of a central unit that processes data, the microprocessor and several components that interact with the outside such as microsensor. At these size scales, the standard constructs of classical physics are not always useful. Because of the large surface area to volume ratio of MEMS, surface effects such as electrostatics and wetting dominate volume effects such as inertia or thermal mass.

INTRODUCTION

MEMS is an emerging technology which uses the tools and techniques that were developed for the Integrated Circuit industry to build microscopic machines. These machines are built on standard silicon wafers
MEMS technology is based on a number of tools & methodologies which are used to form small structures with dimension in micrometer scale.
MEMS are made up of components between 1 to 100 micrometers in size (i.e. 0.001 to 0.1 mm) and MEMS devices generally range in size from 20 micrometers (20 millionths of a meter) to a millimeter

Patterning:
Patterning in MEMS is the transfer of a pattern into a material.

1. Lithography:
Lithography in MEMS context is typically the transfer of a pattern into a photosensitive material by selective exposure to a radiation source such as light. A photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source. If a photosensitive material is selectively exposed to radiation (e.g. by masking some of the radiation) the pattern of the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differ.

 Low cost (can even be made “disposable”)
 FFTs can be used to increase the
performance
 Will work for many machine health
applications
 Onboard signal conditioning. No charge
amplifiers required.

Disadvantages

 Performance still below that of more
expensive sensors
 May not be available in industrial
hardened packages

Summary

 New accelerometers open the door for new
applications in tilt, inertial and vibration
¾ Low cost
¾ High level of integration: Multiple sensors, signal
conditioning
 Clever design can allow use of a less accurate but
less expensive sensor
¾ using microcontrollers for calibration and algorithms
¾ Using signal analysis to improve noise levels
¾ Taking new approaches to traditional problems